message alert on flask code example

Example 1: flask flash

{% with messages = get_flashed_messages(with_categories=true) %}
    {% if messages %}
        {% for category, message in messages %}
            <div class="alert alert-{{ category }} alert-dismissible fade show" role="alert">
                <span>{{ message }}</span>
                <button type="button" class="close" data-dismiss="alert" aria-label="Close">
                <span aria-hidden="true">×</span>
                </button>
            </div>
        {% endfor %}
    {% endif %}
{% endwith %}

Example 2: custom flask messages python

from flask import Flask, flash, redirect, render_template, \
     request, url_for

app = Flask(__name__)
app.secret_key = b'_5#y2L"F4Q8z\n\xec]/'

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/login', methods=['GET', 'POST'])
def login():
    error = None
    if request.method == 'POST':
        if request.form['username'] != 'admin' or \
                request.form['password'] != 'secret':
            error = 'Invalid credentials'
        else:
            flash('You were successfully logged in')
            return redirect(url_for('index'))
    return render_template('login.html', error=error)